1. Field of the Invention
The present invention generally relates to expansion joints for use in coupling conduits that are utilized in conveying gaseous fluids at high temperatures.
2. Description of the Prior Art
In certain conduit installations, it is often desirable to utilize a joint structure for coupling conduit sections together so that lateral or longitudinal movements of the conduits may be effectively accommodated. Such joints are typically known as expansion joints and absorb expansion and contraction movements when vibrations and other relative movements are imparted to the coupled conduits during fluid flow therethrough. Expansion joints have heretofore been proposed in many configurations, such as sheet metal bellows having one or more annular bulges, tubular sleeves and multilayered laminates of various insulating materials.
To be effective, an expansion joint must be capable of accommodating both longitudinal and lateral movements of the coupled conduits, including severe vibrations and other irregular movements. Further, since an expansion joint is often utilized in high temperature applications, it is important that the joint be capable of maintaining its physical integrity in such environments. It is also highly desirable that an expansion joint be capable of resisting the corrosive action of chemicals and providing effective sealing against leaking of gaseous fluids under all anticipated operating conditions.
To provide the foregoing desirable characteristics, an expansion joint has been used which includes a flexible fabric portion bridging the space between the conduit sections and which includes a pair of high temperature resistant fabric layers, such as woven fiberglass cloth, and a foil of super-alloy metal disposed between the two cloth layers. Such a construction is disclosed in applicant's copending application Ser. No. 932,613 filed Aug. 10, 1978.
While the construction as disclosed in the foregoing copending application is effective for the purposes intended, it has been found that the super-alloy foil may become creased, wrinkled or crumpled during handling, installation or disassembly or when the joint otherwise is subject to greater deflections than it would undergo during normal use. This in turn, results in rupture of the foil and loss of its sealing effect. Also, because the foil is not visible, rupture thereof is difficult to detect.
Another drawback in known expansion joints stems from use of erosion shields or liners used in conjunction with the joint. Such a shield or liner is shown in one of the embodiments in applicant's foregoing copending application. The erosion shield or liner protects the fabric component of the expansion joint against constant impingement of hot, dirty gases flowing at high velocity and containing high amounts of particulate matter. During flexure of the expansion joint, folding of the flexible fabric material takes place and pockets are formed between the erosion shield and the fabric material. In power plant applications, in particular, this pocket tends to become filled with ash and soot. When the expansion joint returns to its undeflected position, the ash or soot becomes packed between the flexible fabric material and the erosion shield, and this tends to tear and damage the flexible material of the fabric joint. If the expansion joint is of the type disclosed in applicant's foregoing copending application, the internal foil will also be damaged.